The present invention relates to a belt type continuously variable speed system using a variable radius pulley capable of changing the effective radius of a wound belt.
Conventionally, a belt transmission gear is used for driving auxiliary machines such as a car compressor, an alternator, a water pump, and an oil pump of an automobile.
In the belt transmission gear, a driving force is transmitted at a predetermined change gear ratio through a pulley and a belt from a crankshaft of an engine, and the number of revolutions of each of the auxiliary machines increases as the number of revolutions of the crankshaft increases. The efficiency of each of the auxiliary machines also increases as the number of revolutions thereof increases. Conversely, the efficiency decreases when the number of revolutions is not less than a predetermined number.
Consequently, to rotate the auxiliary machine any more than necessary uselessly expends energy, and also affects the durability of the auxiliary machine. Therefore, a belt transmission gear so adapted that the number of revolutions of the auxiliary machine can be adjusted has been proposed.
For example, there is a belt transmission gear disclosed in Japanese patent publication JP-A-500261. In the belt transmission gear in this publication, a variable radius pulley for changing the effective radius of a wound belt is used.
The variable radius pulley comprises a great number of belt engagement bars arranged in a circular pattern around a rotating shaft and elastically urged outward in the radial direction by urging means. The diameter of the circular pattern is the effective diameter of the variable radius pulley. The effective diameter of the variable radius pulley is changed by collectively moving the belt engagement bars inward in the radial direction against an urging force produced by the urging means.
Specifically, a lot of radial grooves extending in a spiral shape in opposite directions are respectively formed in a pair of rotating plates opposite to each other, and both ends of the belt engagement bar are respectively supported by the corresponding radial grooves of both the rotating plates. Consequently, each of the belt engagement bars can change the effective radius without changing the arrangement in the circular pattern as both the rotating plates relatively rotate. On the other hand, used as the urging means is a helical torsion coil spring interposed between both the rotating plates and rotating and urging both the rotating plates in the direction in which the effective radius is increased.
In the belt transmission gear in JP-A-5-500261, the above-mentioned great number of belt engaging bars are employed for the variable radius pulley, so that the number of components is large. Moreover, the diameter of the circular pattern must be changed in a state where the belt engagement bars are arranged in a circular pattern. Accordingly, the construction of the belt transmission gear becomes complicated. Therefore, smooth speed variation cannot be achieved.
For example, when the great number of belt engagement bars move in order to change the diameter of the circular pattern, frictional resistance is produced between both the ends of each of the belt engagement bars and the corresponding radial groove. Since there are two frictional portions per belt engagement bar, and the number of belt engagement bars is large, there are a lot of frictional portions. As a result, the frictional resistance is increased, thereby making it impossible to achieve smooth speed variation.
The present invention has been made in view of the above-mentioned problems, and has for its object to provide a belt type continuously variable speed system capable of achieving smooth speed variation.
In order to attain the above-mentioned object, in a preferred embodiment of the present invention, a. belt type continuously variable speed system comprises a variable radius pulley for changing the effective radius of a wound endless belt, and a tensioner for adjusting tension on the belt. The variable radius pulley comprises i) first and second pulley main bodies arranged around a rotating shaft and axially movable so that movable toward the shaft, ii) first and second tapered power transmission surfaces formed on opposite surfaces of the first and second pulley main bodies, iii) a power transmission ring interposed between the first and second power transmission surfaces such that it can be eccentric from the axis of the rotating shaft and having said belt wound around its outer peripheral surface, and iv) first urging means for urging the power transmission ring toward a position which is concentric with the axis through the first and second pulley main bodies. The tensioner comprises i) a fixed member, ii) a movable member which relatively moves from the fixed member, iii) a tensioner pulley supported so as to be rotatable by the movable member and engaged with the belt, and iv) second urging means for urging the tensioner pulley through the movable member in the direction in which the tension is given to the belt. At least one of the first and second urging means comprises means for changing the position where the power transmission ring operates. A force produced by the second urging means to make the power transmission ring eccentric from the axis through the belt and a force produced by the first urging means to urge the power transmission ring toward the position which is concentric with the axis are balanced with each other, so that the position where the power transmission ring operates is defined.
In the present embodiment, the power transmission ring is displaced to the position where the force produced by the second urging means in the tensioner to make the power transmission ring eccentric through the belt and the force produced by the first urging means in the variable radius pulley to urge the power transmission ring toward the position which is concentric with the rotating shaft are balanced with each other, to define the position where the power transmission ring is eccentric. Accordingly, the effective radius of the belt is changed. Speed variation is achieved using the balance between the forces through the belt, thereby making stable and smooth speed variation possible.
The second urging means may, in some cases, comprise an elastic member for giving the tension to the belt through the tensioner pulley, and an actuator for actively changing the position where the tension pulley operates through the variable member so as to adjust the tension on the belt.
In this case, it is preferable that a force produced by the elastic member in the tensioner to make the power transmission ring eccentric through the belt is smaller than a force produced by the urging means in the variable radius pulley to urge the power transmission ring toward the position which is concentric with the axis. The actuator may, in some cases, be a hydraulic actuator such as a hydraulic cylinder or a hydraulic motor. Further, the actuator may, in some cases, be an electric motor.
The first urging means may, in some cases, comprise an elastic member for urging the first and second pulley main bodies in the directions nearer to each other, and an inertia member displaced in the centrifugal direction depending on the rotational speed of the variable radius pulley to urge the first and second pulley main bodies in the directions nearer to each other, and the second urging means may, in some cases, comprise an elastic member for giving the tension to the belt through the tensioner pulley.
In this case, it is preferable that the force produced by the elastic member in the tensioner to make the power transmission ring eccentric through the belt is larger than the force produced by the elastic member in the variable radius pulley to urge the power transmission ring toward the position which is concentric with the axis. The elastic member in the first urging means may be a coil spring or a Belleville spring. The inertia member may, in some cases, be arranged in a containing space which narrows outward along the radius of the variable radius pulley.
The first urging means may, in some cases, comprise a hydraulic actuator such as a hydraulic cylinder or a hydraulic motor or an electric motor as means for changing the position where the power transmission ring operates.